Determination of the Relationship Between Bacterial Coculturing, Antibiotic Resistance and Bacterial Growth

Date of Award


Degree Name

M.S. in Chemistry


Department of Chemistry


Advisor: Matthew Lopper


Antibiotic resistance is a problem facing the world in the twentieth century as a high number of people are killed by bacterial infections with no working antibiotic. Antibiotics are produced by bacterial strains in an attempt to fight off other strains competing for the same resources. One way that bacteria strains become resistant to antibiotics is by effluxing the antibiotic compounds through an efflux pump. This thesis focuses on finding a way to combat antibiotic resistance. Using a strategy of coculturing two bacteria strains together, various supernatants were tested to determine if any secondary metabolites were produced by either strain that increases the susceptibility of Escherichia coli (E. coli) to the antibiotic levofloxacin. The supernatants were first tested in an efflux assay where the amount of ethidium bromide effluxed from E. coli was measured through fluorescence. Positive supernatants were then tested in a growth assay to test the supernatant's effect on the susceptibility of levofloxacin on E. coli. The supernatant of the coculture between Streptomyces griseus (S. griseus) and Paenibacillus polymyxa (P. polymyxa) showed an increase in fluorescence, meaning a decrease in the efflux activity of ethidium bromide from the cell. Once tested in the growth assay, E. coli showed no increase in susceptibility to levofloxacin when grown with the supernatants. However, when testing it was determined that an unknown compound was causing E. coli and P. polymyxa to enter log phase growth sooner than the controls. It was presumed through dialysis and heat deactivation that the unknown secondary metabolite causing this shift was likely an unknown peptide produced by S. griseus.


Biochemistry, Antibiotic Resistance, Antibiotics, Bacterial Competition, Streptomyces griseus, Paenibacillus polymyxa

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